1. Field of the Invention
The invention relates to a driver assistance system and, more specifically, to a system applying a torque based on a reliability determination.
2. Description of Related Art
Numerous concepts in the field of driver assistance systems help a driver of a motor vehicle; in particular, such systems may assist the driver in potentially hazardous situations. Such systems may directly engage specific functions of the vehicle or may give the driver a suggestion regarding vehicle control. Known examples of such driver assistance systems are ESP (electronic stability program) and ABS (anti-lock braking systems). These systems normally monitor, using suitable sensors, the present state of the vehicle, for example, wheel speeds, yaw rate, velocity and acceleration, etc. Other systems, for example, parking assist or brake assist, also monitor the surroundings of the vehicle using cameras, ultrasound sensors, radar sensors, lidar sensors, or the like.
In important situations, some assistance systems help vehicle steering. In such a situation, the system may superimpose, in addition to the normal steering assistance by a steering torque produced by a power steering control unit corresponding to the steering movement of the driver, a corrective steering torque to either strengthen or weaken the steering movement given by the driver. In addition the system a may suggest an adaptation of the steering angle to the driver using a detectable force in the steering wheel.
Imposing more torque into the steering is desirable only on recognizing a potentially hazardous situation with sufficient reliability. Otherwise, incorrect recognitions lead to driving behavior of the vehicle that is unpleasant and/or unacceptable to the driver. Improved sensors or an improved analysis of the sensor signals may cut this problem. In addition, analyzing input signals from two independent sensors may help recognize the hazardous situation, so that an increased level of security results due to the redundancy.
In addition, the corrective steering torque and the rate of change over time thereof are limited, to prevent the driver from feeling a sudden, strong steering torque in the steering wheel with an incorrect recognition, which could irritate the driver or cause the steering wheel to slips away from the driver. Using a more or less “soft” increase of the steering torque, well controllable by the driver, lets the driver override any increase of steering torque. Sometimes where fractions of a second could be decisive, the full steering torque is not available promptly, because the system reacts sluggishly.